I'm in almost the exact same situation as you! Scored a 39Q and 41V, and my total score is above the median for the schools I'm applying to. However I think I can do better in math and I'm taking the exam again in a few weeks. I am concerned that my verbal will go down (I wasn't doing THAT well in practice exams) and my math will stay around the same.
Heres's my solution/advice and what I did. Since your first score is solid, send your score report to all the schools you are applying to. Take the exam again, and send no score reports the day of the exam. If you are happy with your new score, then send the updated report. If you are not happy, don't send it, and the school will never know you bombed the 2nd time around.
My only question. Say my total score goes down 10-30 pts, but my Quant goes up. I'm not sure if I would send the updated scores. On one hand, my overall score will be lower. But on the other hand, my new quant could show them I'm capable. Thoughts?